The invention relates to easy-to-assemble structures, and more particularly to easy-to-assemble structures having gravity-controlled locking engagements between their components.
The invention has wide educational, household, commercial, industrial, . . . uses. While not limited thereto, it is herein described mostly in connection with a seat or bench, a (telephone or voting) booth, and a carrel-table assembly for the library study.
The ordinary library carrel-table assembly is very complicated in design but weak in structure. Usually the assembly is made of several pieces of 3/4 inch plywood assembled together by means of angle irons, brackets, tension bolts, nuts, wood screws, and the like arranged in unsightly manners. The number of these fastening devices is amazingly large. Not infrequently, there are over 60 or 85 screws or bolts to be meticulously assembled into the structure. The assembling operation typically takes two skilled persons approximately 11/2 hours. Often, these persons have to spend several hours just to understand the assembly instructions alone.
The steel bolts and screws are by no means the best fastening devices for the purpose. The wood between the screw threads are easily stripped. The hole for a screw is often enlarged, thereby loosening the screw grip and hastening the stripping process. This condition soon renders the screw useless as an effective fastening device. Load on the structure is then shifted, with increasing intensity, to the other screws or bolts. Again and again, the loosening and stripping processes are reinitiated with increasing rapidity until complete, catastrophic failure of the carrel occurs.
Many of the screws are often located in hard-to-reach places. They are often designed to intersect the plywood surfaces at acute angles far from 90.degree.. Such designs invariably result in weak structural joints. In addition, the many angle irons, screws, bolts, and nuts used on the ordinary carrel often protrude out of the plywood. They are thus unsightly and unsafe. The weight of the numerous fastening devices is often another undesirable factor to consider.
In summary, the conventional carrel is complicated in design, weak in structure, heavy in weight and, furthermore, unsightly to see, unsafe to use, time consuming to assemble, and costly to install.